Machine and method for shrinking sheet metal to form curves



J. HAMLIN 2,230,490

MACHINE AND METHOD FOR SHRINKING SHEET METAL TO FORM CURVES Feb. 4, 1941.

2 Shets-$heet l Filed March 8, 1939 L/OIYIV bm/u/v Feb. 4, 1941;

J. HAMLIN MACHINE AND METHOD FOR SHRINKING SHEET METAL TO FORM CURVES Filed March 8, 1939 2 Sheets-Sheet 2 .Zzaen 1 Aoziiys- Patented Feb. 4, 1941 UNITED STATES PATENT OFFICE MACHINE AND ME'rnoD FOR SHRINKING SHEET METAL TO FORM CURVES 13 Claims.

There are a multitude of various operations on thin flat sheets of metal to change these into curved forms, some of the curves being fairly simple, such as concave on one side and convex 5 on the other in a more or less straight line direction. Other curves are more complicated and might be considered as having curves in various planes intersecting the sheet metal forming in effect dished sheets concave on one side and convex on the other side in all directions. Considerable difficulty and a great deal of hard work is required especially in curving the thin sheet metal forming the cover or outside surface of aeroplanes, as in the fuselage, the wings, ailerons and other parts of the construction. There are some preferred types of metal which are very diflicult to work such as the metal duraluminum designated in the trade as dural and various sheet metals having a fairly large percentage of aluminum in a composition. Some of these metals are quite brittle, and do not. draw in presses in a manner similar to steel or alloys having the base of copper or similar metals. In the present practice of curving some of these 25 metals, a great deal of the work is done by hand,

the workman using a hammer and operating over a suitable anvil. In other types he employs power hammers which are substituted for the hand hammers,'but even this work is not accurate and skilled workmen.

An object and feature of my invention relates to a machine and the method by which in a press the thin sheet metal may be operated on to form 35 distorted rib and groove construction and this is then flattened which causes a pulling in of the metal and thus depending upon the number of the flattened ribs and grooves causes a curving of the sheet metal. The action in 'reality de- .40 velops a slight upsetting or thickening of the press and by means of a mandrel the groove and rib formed in the sheet metal is supported while 5 it is subjected to a rolling action of a roller operrequires a considerable time as well as highly ating over the rib and groove starting at its disappearing end, then as the rib and groove on the sheet metal is rolled flat, the supporting mandrel is retracted, thus bringing the rib and the groove formed in the sheet metal into the plane of the sheet immediately adjacent thereto. Incidentally in my invention one rib is formed by the die pressing, the roller is located in a position to immediately roll the previously formed groove and rib to the flat while the sheet metal is firmly held between the anvil and the pressure block.

Another feature and characteristic of my invention is that the anvil which is preferably slightly convex on its upper surface considered from side to side has a die preferably a half circle or oval in cross section or any other similar curved form, this gradually decreasing in cross sectional area, however on the same axis until the die merges with the upper surface of the anvil. This in cooperation with the pressure block which has a complementary recess or groove forms the groove and rib in the sheet metal, the groove being considered cn-the lower side which rests on the anvil and the rib formed on the upper side, the sheet metal being however of uniform thickness and as the action is to roll the rib flat, such double groove and rib in the sheet metal is hereunder designated merely as a rib.

, The conjoint feature of the invention is providing a carriage which is movable on the pressure block and in such carriage there is mounted the pressure or rib flattening roller. This must be positively rotated in order to prevent any slippage on the upper surface of the sheet metal and therefore a further characteristic of my invention is in providing the carriage with a rack and having a pinion connected to the roller meshing with the rack. Therefore when the carriage is given a positive movement rolling over the anvil, the roller is positively rotated. Cooperating with the rib and the roller, the carriage also shifts an anvil which is the same cross section and shape as the die and hence fits in the groove of the sheet metal formed by the prior die action. Therefore when the roller bites downwardly on the rib, the sheet metal being held clamped by the anvil and the pressure block and My invention also comprehends the method of operating on sheet metal in that there is first formed a rib extending into the sheet from one edge and this rib tapering or vanishing remote from the edge. Then while the sheet metal is held from slipping, the rib is rolled fiat startin from the end remote from the edge and the rolling action continuing to the edge of the sheet. Further in such action the rib is partly supported, the support moving at the same speed and simultaneously with the rolling action. A characteristic of the action of the equipment on the metal is somewhat diificult to analyze but apparently in the die pressing to form the rib the metal is first distorted and the portion at both sides of the die are brought slightly closer together until the full size rib is made and the sheet firmly gripped between the anvil and the pressure block. This action of forming the rib therefore slightly shortens the distance on the edge and the edge portion of the sheet across the base of the rib from the original position of the particles of metal which are bent to form the rib. Then in the action of flattening the rib, the formerly displaced metal is pressed downwardly into the plane of the adjacent portions of the sheet. This causes a very slight thickening of the sheet at the part made into the rib and forces a small amount of the metal beyond the original edge line of the sheet a very slight distance. In view of the fact that there is a distinct difference in the treatment and operation on the metal known as dural or equivalent alloys, care must be taken to operate in the proper direction in accordance with the so-called grain of the metal.

My invention is illustrated in connection with the accompanying drawings, in which:

Fig. 1 is a side elevation of a suitable press and may be considered as taken in the direction of the arrow l of Fig. 2 or Fig. 3.

Fig. 2 is a plan taken in the direction of the arrow 2 of Fig. l.

Fig. 3 is a vertical section taken on the line 33 of Fig. 1 in the direction of the arrows, this showing part of the machine in edge elevation.

Fig. 4 is a longitudinal vertical section taken on the line 44 of Fig. 3 in the direction of the arrows and on a larger scale.

Fig. 5 is a vertical transverse section on the line 5-5 of Fig. 4 in the direction of the arrows.

Fig. 6 is a horizontal section on the lineG-B of Fig. 3 in the direction of the arrows when the pressure block is in its elevated position.

Fig. '7 is a plan on a reduced scale illustrating the transforming of a fiat sheet of metal to the curved and shrunk form.

My. machine need not be restricted to the specific design as shown but in this I employ an anvil II which is made in the manner of a heavy metal block. This anvil has the characteristic of an upper or working surface l2 which is illustrated as being curved slightly convex considered from side to side, the sides being indicated by the letter S. The working surface is on a straight line considered from the front edge l3 to the rear edge M on any line parallel to the edges. The front I5 is curved outwardly with a convex curvature, thus there is a slight curved bevel I5 between the two corners IT at the termination of each of the sides. The anvil block has a lowered portion 18 adjacent the back and on this there is mounted a guide block 19 attached to the anvil in any suitable manner or formed integral therewith. The die 25 which may be formed integral with the anvil or of a separate piece of metal attached thereto is indicated as being half circular in cross section above the working surface of the anvil. The center or axis of the die is indicated at 26. It is not necessary that this be strictly half circle in cross section as it may vary slightly to form in effect a half oval, however this die may be considered as having a transverse rneasurement 21 along the surface of the working face and a height measurement 28 above the working surface of the anvil. A characteristic of the die is that it tapers and vanishes into the surface [2, that is, as the transverse measurement 21 decreases. the vertical height 28 also decreases. The die is therefore substantially half-cone taken through the apex and the base on a plane through the axis. It will be understood however that instead of any line being straight from the apex to the base this may have a slight curvature and there may be quite a deviation in the types of dies depending upon the contour and shape of the groove and rib to be formed in the sheet metal. The base portion of the die indicated at 29 is shown in alignment with the rear face 30'of the anvil and this tapers to the apex 3!, note particularly Fig. 4.

In the illustration the anvil is shown as being connected to a frame 35 which has a lower arm 36 forming the base of the machine and connected to the anvil a vertical position section 31 and an upper arm 38. The upper arm has a substantial guide block 39- forming a guide for vertical travel of the pressure block 40 which is supported and actuated by two stems 4| reciprocating vertically in the vertical guides 4|. A piston rod 42 is connected by a cross head 42' to the stem 4|. This piston rod may be operated by compressed airor any suitable type of power plant.

The characteristics of the pressure block are that it has a lower working face 45, the main portion of which is complementary to the working face I2 of the anvil, that is, it has a concave curve considered from side to side and on any line parallel to the axis, such line is straight. There is a slight downward bevel curve corresponding to the bevel H5 The pressure block it will be noted has its front face 46 projecting considerably in front of the front face l5 of the anvil, the reason being as hereunder described. The pressure block is provided with a conical groove 41 which is complementary to the die 25. This groove thus tapers and vanishes in the working face of the pressure block forming in effect a half cone, the die and the groove must be proportioned to accommodate the thickness of the sheet metal to be worked in a machine.

The pressure block has an opening 50 from its front to its rear face, such opening having a top 5| and two opposite sides 52. From these sides there are two recesses 53 and beyond the recesses upper and lower V shaped grooves 54 and 55 forming tracks and the extreme sides of the opening are formed by the vertical faces 56. Rack teeth 51 are formed on the lower face of the recesses 53 on each side of the main portion of the opening and contiguous to the side faces 52. Slidably mounted in the opening 50 there is a carriage 50. Such carriage has two parallel guide arms 6| each having a V shaped guide edge 62 operating respectively in the longitudinal V shaped tracks 54 and 55. The side face 63 of each of the guide arms forms a snug but sliding fit with the vertical face 56 forming the extreme width of the main opening. These guide arms The opposite end of the carriage and attached to the arms is a cross head 66. This has a vertical slot 61 therein to engage the mandrel designated "I5. This mandrel is the same shape in cross section as the die 25 and is thus substantially half of a cone in which the base I6 may be considered the large end contiguous to the rear face 30. The portion beyond this base is a half cylinder, this being the part 11 which operates in a sliding manner through the guide block [9, this block having a guide opening 18 of similar cross sectional shape. It is essential however that the lower surface 19 of the guide opening be flat and be in alignment with the upper surface of the working face I2 of the anvil on which the mandrel lies. Such mandrel rests on the working surface [2 and has its apex 80 extending substantially as far as the apex 3| of the die 25. The mandrel has a neck 9| extending through the vertical slot 61 and is provided with an inner and an outer collar'82 and 83 having a snug fit on each side of the cross head 66 but with sufiicient play to allow up and down movement of the neck and thus the mandrel in the guide slot.

The pressure roller .assembly 90 employs a shaft 9|, which is journaled in the arms 8|. Secured to this shaft there are two pinions 92 which fit in the recesses 53 and engage and mesh with the rack 51. A pressure roller 93, this being cylindrical from end to end, is fitted in the central part of the opening 50. There is provided a clearance between the top of the roller and the top 5| of the opening and a rather close working fit of the sides 94 of the roller and the faces 52 of the opening 50.

The manner of operation and functioning of the machine is substantially as follows: The pressure block 40 is raised by any suitable mechanism so that there is a clear space between the underside of the pressure block and the working face I2 of the anvil as shown in Figs. 1 and 2. The sheet metal to be worked is then inserted between the anvil and the pressure block with the edge positioned spaced inwardly from the rear edge 30 of the anvil, this being so that such edge does not extend beyond the base portion 29 of the die 25. The carriage 60 is retracted in the position indicated in Figs. 1 and 4 so that the roller 50 is located beyond the line from the apex 3| of the die parallel to the rear edge 30 of the anvil. The pressure die is then forced downwardly under pressure on the sheet metal and such metal is first gripped between the die 25 and the complementary groove 41 on the underface' of the pressure block. The continued downward pressure then causes a slight slippage of the- 7 there can be no slippage or movement of the sheet relative to the anvil or the pressure block and the metal is gripped tightly between the die and the complementary. conical groove 41. The formation ofthe conical rib in the metal is then completed. This is the operation for forming the first rib in the sheet.

The succeeding operation while maintaining the carriage and roller in its retracted position is to raise the pressure block so that the sheet may be moved. Then it is shifted laterally so that the carriage.

the rib form in the sheet fits over the conical mandrel I5. is flat on its undersurface and rests on the straight line surface of the anvil. The rib as above mentioned is made to have a snug fit over the mandrel. In fitting the sheet this likewise positions the inner edge of the sheet in proper relation to the rear edge 30 of the anvil and the base 29 of the die 25. The pressure ,block is then again forced downwardly whilemaintaining the rib of the metal fitted over the mandrel and this causes a second gripping of. the sheet between the die 45 and the complementaiy groove 41 and forms a second rib spaced parallel to. the first rib as the die and anvil have their axes parallel and shown in Fig. 6. On completion of the pressure stroke which brings the pressure block and anvil into the position of Fig. 4 relative to the sheet placed between the two, the sheet is thus firmly gripped and cannot slip in any direction. While retaining the pressure block in its lower position, the carriage is then forced towards the rear side of the machine from its retracted position of Fig. 4. As above mentioned when in this retracted position the bottom of the roller 93 which is in alignment with the immediate portion of the underside 45 of the pressure block 40 is also positioned slightly beyond the apex end 80 of the mandrel and thus slightly beyond the place at which the apex of the rib of the metal merges into the flat and undistorted portion of the metal sheet. On the inward movement of the carriage the roller is positively rotated by the intermeshing of the 'pinions 92 with the rack 51. In practice the racks are made of a separate strip of metal from the heavy block which forms the pressure block andthus may be properly fitted in position and made and renewed without any trouble. During the retracting movement of the carriage the mandrel is also pulled outwardly from within the rib of the sheet metal due to the interaction of the collars 82 and 83 with the cross head 60, the mandrel sliding in the slot 61' and thus permitting the free up and down movement of the pressure block without any lifting of the mandrel, the mandrel of course being positively guided in the guide block l8. The roller then flattens the rib, pressing this downwardly as it advances over the conical rib, the distortion of the rib causes this to press downwardly against the mandrel as the mandrel recedes. Of course as the mandrel is conical and itis fitted in'the conical groove side of the rib of the sheet metal, as such mandrel recedes towards the open end of the groove there is a space between the mandrel and the inside of the oove in the sheet metal. However the metal This mandrel as abovementioned bends downwardly and isfiattened in somewhat of a gradual curve from the transverse line on which the periphery of the roller 93 grips the upper surface of the sheet on each side of the rib and centered over the rib. Thus as there is the simultaneous recession of the mandrel accompanied by the advance of the pressure roller, there is no danger of the rib of the sheet metal on being pressed downwardly gripping, the mandrel so tight as to block or prevent operation of The carriage is completely retracted until the roller completes its stroke to the base of therib, that is, at the edge of the sheet and hence the rib is completely flattened from its apex to its base. As above mentioned this fiattening action of the rib causes a very slight thickening of the sheet metal at the portion formed into the rib and also causes a slight swell- Figs. 1 and 4, the pressure block raised, the sheet metal is shifted to bring the second formed rib in alignment with the mandrel and a third operation carried on. It is obvious that when a rib is once flattened it engages between the complementary working faces of the anvil and pressure block just the same as any other part of the sheet metal. Thus at each stroke a new rib is formed in the sheet metal and by the complementary action of the carriage and roller a rib is rolled flat. It will thus be seen that consider able speed may be developed in curving the sheet material. It is obvious that where it is necessary to have the ribs close together for a quite pronounced curve that the roller may be of less width on its face and the die and mandrel positioned closer together. Likewise where it does not require so many ribs to give the curvature these can be positioned wider apart or in operation fewer ribs are formed in the sheet.

In Fig. 7 I attempt to illustrate the shrinking of a sheet in which the sheet metal is indicated by the numeral I00 and before treatment has the end edges IOI and I02 and the side edge I03, these being indicated as dotted. The series .of half conical ribs indicated at I04 in dotted lines are as above mentioned developed in a sequence and then flattened without wrinkling. This causes the edge I03 to be forced somewhat outwardly as indicated at I03 and there are a series of very slight end bulges I05, being one for each of the ribs. In the drawings theseare shown as exaggerated. The edges I02 are pulled into the line WI and I02. At the same time the sheet is given a curvature to the desired shape and degree either in one or two directions depending upon the particular type of article to be formed by shrinking the sheet. After the sheet is shrunk to the desired shape it is then given a final smoothing by operating in a hammer press, this however is not for the purpose of further shrinking the metal but to bring all of the parts of the sheet in the proper smooth curve. If desired the sheet may then be burnishedor polished to have the same finish as the untreated portion of the sheet. The rib formed in the sheet metal at any cross section should have a gradual merging curve into the body of the sheet. This is accomplished by providing the die 25 with a slight fillet at each edge and also the mandrel I5 with a similar fillet.

Various changes may be made in the details of the construction without departing from the spirit or scope of the invention as defined by the appended claims.

I claim:

1. In a device as described, the combination of an anvil having a slightly convex upper working surface considered transversely, a tapered die extending above such working face, a reciprocating pressure block having a tapered groove complementary to the die, the pressure die having an opening therein from the front towards the rear, a carriage slidably mounted in said opening and operating on a track, a pressure roll journalled in the carriage, a gear connected to the pressure roll, a stationary rack meshing with the gear connected to the pressure block, means to reciprocate the pressure block and press such block downwardly to form a tapered rib in sheet metal and at the same time to grip the sheet metal between the anvil and the pressure block whereby a prior formed rib may be positioned in the line of travel of the pressure roll and means operative while the anvil and pressure block grip the sheet metal to move the carriage and hence rotate the roll in contact with the prior formed rib to thereby flatten such rib into the plane of the sheet metal on each side of the rib.

2. In a device as described and claimed in claim 1, a mandrel having a parallel sided portion with a slidable mounting in a guide and having another portion tapering to conform to the taper of the die and to fit in a'rib formed by the said die and groove, the mandrel and the anvil having complementary engaging faces, the anvil forming a support for the mandrel, a vertically slidable connection between the mandrel and the carriage and a thrust and pulling connection between the mandrel and the carriage to permit raising of the pressure block without upward movement of the mandrel and to move such mandrel for insertion in the underside of a rib of sheet metal and to withdraw such mandrel as the pressure roll operates over a rib.

3. In the method of shrinking sheet metal to form curves comprising die pressing sheet metal to form a tapering bead in which the apex of the bead is remote from the edge and merges into' the plane of the sheet, then in the subsequent operation gripping and holding the metal of the sheet on opposite sides of the bead on a surface to prevent slippage, internally supporting the bead on such surface on its underside and rolling the metal of the bead without slippage from its apex towards the edge of the sheet and simultaneously withdrawing the support whereby the material forming the bead is pressed into the glarcile of the sheet immediately adjacent the 4. In the method of shrinking sheet metal to form curves comprising die pressing the 'sheet to form a hollow bead shaped as a segment of a cone with the base at the edge of the sheet and the apex remote therefrom, thereby shrinking the sheet met-a1 at any diametrical section of the partial cone a measurement substantially equal to the radius of the hollow rib in the plane of the sheet, shifting the sheet and gripping the same on the upper and lower surface and on opposite sides of the hollow bead to prevent slippage of the sheet supporting the hollow side of the bead from the base towards the apex, rolling the metal of the bead without slippage from its apex towards the edge of the sheet and simul-.- taneously withdrawing the support of the hollow side of the bead whereby the material forming the bead is pressed into the plane of the sheet immediately adjacent any and all transverse sections of the bead.

5. In the method of shrinking sheet metal having a tapering rib, the apex of the rib converging into the sheet of metal and the rib enlarging gradually. towards an edge of the sheet comprising gripping the sheet on opposite sides of the rib to prevent slippage and at the same time supporting the underside of the rib, then in a rolling action working from the apex of the rib towards its base flattening the rib into alignment with the sheet metal adjacent thereto and at the same time withdrawing the under support of the rib whereby the sheet metal is shrunk in the portion forming the rib.

6. In a device as described, the combination of an anvil having a continuous working face, a pressure means having spaced working faces,

means to grip and hold sheet metal between the respective faces of the anvil and pressure means whereby a rib in the sheet metal tapering from its large end adjacent one edge to a small end towards the opposite side of the sheet may be located between the spaced surfaces of the pressure means and means to exert a moving pressure contact on the rib between the spaced working surface and the anvil towards one side of the anvil whereby the rib may be flattened in a progressive manner from the small end towards its larger end,'a mandrel supported on the working face of the anvil and having a contour to conform to the underside of the rib and fitted therein and means to withdraw the mandrel from under the rib as the moving pressure contact device operates over the rib.

'7. In a device as described, the combination of an anvil having an upper working face terminating at the front of the anvil, a pressure block having two complementary working faces with an opening therebetween, means to relatively move the anvil and pressure block to grip sheet metal between the working face of the anvil and the two spaced working faces of the pressure block to restrain such sheet from movement whereby a sheet having a tapering rib merging at its apex in the sheet may have the rib located in the said opening between thetwo working faces of the pressure block, a roller movably mounted to operate through the said opening of the pressure block to engage the rib commencing at the apex end and by a movement over the anvil flatten the rib to align with the working face of the anvil located in the said opening of the pressure block to thereby shrink the metal forming the rib, a mandrel having a flat undersurface resting on the working face of the mandrel and having an upper face conforming to the shape of the underside of the rib and fitted therein, means interconnecting the mandrel and the roller to retract the mandrel from under the Ilb as the roller progresses over the rib.

8. ma device as described, the combination of an anvil having a top working face terminating at the front of the anvil, a pressure block having two spaced working faces on its underside with an opemng from the front towards the rear of the pressure block, a mandrel having a flat undersurface resting on the working face of the anvil 1n the said opening, the mandrel having a tapered upper surface converging to an apex, means to move the pressure block towards the anvil to girp a sheet of metal having a rib tapermg from one edge to an apex'in the plane .of the sheet whereby the mandrel fits in the underside of the rib and the sheet is gripped to prevent movement between the working face of the anvil and the two spaced working faces of the pressure block, means to produce a moving pressure contact-with the rib in the said opening between the pressure block and the anvil moving from the apex of the rib towards the edge of the sheet and means to simultaneously retract the mandrel 5 whereby the mandrel partly supports the rib while the pressure means flattens the rib to align ment with the working face of the anvil underneath the retracted mandrel.

9. In a device as described, the combination of 70 an anvil having a working face with a tapering rib forming a die, a pressure block having two working faces, one of which has a tapering groove complementary to the die, means to move the pressure block towards the anvil and to exert a pressure to form a tapering rib in sheet metal between the tapering die and the tapering groove, the pressure block having an opening between its two working faces, a carriage having a roller movably mounted therein, the pressure block and anvil being adapted to grip sheet metal on opposite sides of a tapering rib with the rib located in the said opening and simultaneously form a second rib in the sheet metal, means to develop a rolling contact between the roller of the carriage and the sheet metal to flatten the rib located in the said opening to alignment with the working face of the anvil aligned with the said opening, a mandrel having an underface shaped to conform to the working face of the anvil having an upper side to conform to the underside of a rib in the sheet metal, the mandrel resting on the anvil and under a rib of the sheet metal located in the said opening, means connecting the mandrel with the carriage whereby on movement of the carriage and the rotating movement of the roller, the mandrel is shifted over the face of the anvil and withdrawn from underneath the rib of the sheet metal, the mandrel partly supporting the rib while the roller flattens the rib into alignment with the sheet metal on opposite sides thereof.

10. In a device as described, the combination of means to die press a tapering rib in sheet metal, such rib extending from one edge of the sheet and tapering to a vanishing end at its apex remote from such edge, an anvil having a supporting surface for the sheet and means to press the rib into the plane of the sheet at any portion adjacent such rib, the pressure means having a moving surface contact engaging the rib from its apex towards its base at the edge of the sheet, a mandrel having substantially the same cross sectional and, longitudinal shape as the rib, the mandrel having a surface resting on the anvil under the rib and means connected to the pressure means to retract the mandrel at the same speed as the moving surface contact of the pressure means and the rib.

11. In a device as described, the combination of means to die press a tapering rib in sheet metal, such rib extending from one edge of the sheet and tapering to a vanishing end at its apex remote fromsuch edge, an anvil having a supporting surface for the sheet and means to press the rib into the plane of the sheet at any portion adjacent such rib, the pressure means having a moving surface contact engaging the rib from its apex towards its base at the edge of the sheet, a mandrel having substantially the same cross sectional and longitudinal shape as the rib, the mandrel having a surface resting on the anvil under the rib, the pressure means including a roller, means to move such roller over the rib from the apex towards the base end and means to positively rotate the roller at its peripheral speed of contact with the rib and means connected to the pressure means to simultaneously retract the ma drel as the pressure roller advances over the rib whereby the mandrel is withdrawn from the rib simultaneously with the flat pressing of the rib.

12. In the method of shrinking sheet metal in which a tapering bead is formed in sheet metal comprising holding the sheet metal on opposite sides of the bead against a surface to prevent slippage of the sheet, supporting the bead on the underside above the surface, applying a pressure on the upper surface of the bead from its apex continuing towards its base and at the same time discontinuing the support of the head to working face of the anvil, a pressure roller, means to move said roller over the anvil to contact and press the rib from the vanishing rib towards the edge whereby the metal of the ribaligns with the portion of the sheet held between the anvil and the pressure block, the pressure roller being mounted in a carriage and such carriage being slidable transversely in the pressure block, a mandrel operatively connected to such carriage, such mandrel having a cross section and longitudinal shape corresponding to the underside of the rib, the mandrel and the working face of the anvil having complementary faces to support the mandrel, the said mandrel being retracted from inside of the rib simultaneously with the movement of the pressure roller over the rib whereby the mandrel gives a partial support to the rib as it is pressed flat.

JOHN HAMLIN. 

